Valves are common components of almost any piping system. Although they can be constructed in many different configurations and sizes, a typical valve will include a few basic elements. These include: a valve body that houses internal components within an internal cavity; inlet and outlet pipes leading to and from the valve body; and a valve member that is positioned within the cavity of the valve body. These components are attached such that fluid entering the valve through the inlet pipe is either allowed by the valve member to flow therethrough to the outlet pipe or prevented from such flow based on the position and/or orientation of the valve member within to the valve body.
In many instances, the valve member of a valve is a rotatable structure, such as a ball or frustoconical plug, that includes a passageway through which fluid can flow. Rotation of the valve member moves the passageway from an orientation aligned with the inlet and outlet pipes (in which fluid can pass through along a flow axis) and an orientation perpendicular to the flow axis (in which fluid flow is blocked). Often valves that employ a rotating valve member include structures on the valve member (or a component attached thereto, such as the valve stem or adapter) and the body that interact to control the degree of rotation of the valve member. For example, many valves are designed to rotate through only 90 degrees between the open and closed positions, with further rotation being prevented by stops located on the upper portion of the body and the lower surface of the adapter.
Valves can be formed of a variety of materials, including both metallic and polymeric materials. Valves formed of polymeric materials can be advantageous in many pipeline environments; they do not rust or corrode, they are typically lighter weight than metal valves, they can be quickly welded into place when the pipelines are also formed of a polymeric material, and often the pieces of the valve (and in particular the valve body) can be molded in an injection or compression molding process rather than requiring extensive machining.
Although they enjoy the foregoing advantages, polymeric valves typically require several assembly steps. Of course, the configuration of components formed of polymeric materials is limited by the practicalities of the molding process. As a consequence, if the valve body is injection or compression molded, it is generally molded in two or three separate pieces that are joined in a subsequent welding or fusion operation. The valve member and accompanying stem and adapter (which facilitate rotation of the valve member) are typically formed of separate pieces that are assembled in a subsequent operation (usually after the valve member has been placed inside the valve body pieces and they have been fused). All of these post-molding assembly steps can add cost to the finished valve. Also, it may be desirable that the valve include structure that halts rotation of the valve in desired positions; if so, these structures are also subject to the practical limitations of the molding process.